Modem aircraft are often powered by a propulsion system that includes a gas turbine engine housed within an aerodynamically streamlined nacelle. The major engine components include a fan section comprising a rotatable hub, an array of fan blades projecting radially from the hub and a fan casing encircling the blade array. During engine operation it is possible for a fan blade to become separated from the hub or for part of a blade, which may comprise substantially the entire blade, to become separated from the remainder of the blade. One function of the fan casing is to contain these potentially hazardous fragments.
For small diameter engines, adequate containment capability can usually be achieved with a metallic case thick enough to resist penetration by a blade fragment. However for large diameter engines, a metallic case thick enough to resist penetration is prohibitively heavy. Therefore, it is customary for manufacturers of large diameter engines to employ a fabric wrapped containment system comprising a light weight, high strength ballistic fabric such as KEVLAR.RTM. Bar (a trademark of E.I. DuPont de Nemours & Company) wrapped in multiple layers around a relatively thin, penetration susceptible support case. In operation, a separated blade fragment penetrates the support case and strikes the fabric. The fabric deflects radially, and at least some of the fabric layers remain intact to capture and contain the fragment.
Although fabric wrapped containment systems are far more weight efficient than metallic containment cases, they nevertheless add considerable weight to the engine. Furthermore, if the fabric deflects excessively, the fabric enshrouded blade fragment can strike and damage the interior of the nacelle. Therefore it is desirable to deploy the fabric on the support case in a way that minimizes weight without compromising containment capability or risking damage to the nacelle.